There is a rapid spread of devices compliant to wireless local area network (hereinafter, LAN) such as IEEE 802.11b standard established by the Institute of Electrical and Electronics Engineers based in the United States. Also, it is expected that a seamless network society will arrive where audio visual (hereinafter, AV) devices are connected with personal computers by a wireless network or other means. With this background, there is a demand for a technique to produce small and high-speed data communication devices at low cost.
As an approach to the technique, a communication system called Ultra Wide band (hereinafter, UWB) using a pulse-like modulation signal is drawing attention.
FIG. 11 is a block diagram of a UWB wireless device as an example of a conventional communication device. This conventional example includes a plurality of receiving systems. Antenna 1001 receives a signal, and amplifier/filter 1002 amplifies and filters the signal to remove unwanted signals. Automatic gain controller (hereinafter, AGC) 1003 controls the gain of the signal, and receiver systems 1011A and 1011B receive the gain-controlled signal. In receiver systems 1011A and 1011B, mixers 1004A and 1004B correlate the gain-controlled signal from AGC 1003 with pulse signals generated by pulse generators 1007A and 1007B, respectively.
Filters 1005A and 1005B filter the signals from mixers 1004A and 1004B, respectively, to remove unwanted signals. Analog/digital (hereinafter, A/D) converters 1006A and 1006B convert the filtered signals to digital signals. Controller 1010 determines the correlation and improves the correlation by controlling the timing of timing generators 1008A and 1008B with clock control signals and performing synchronization acquisition and holding of the signals received from controller 1010 and signals from local oscillation (hereinafter, LO) generators 1009A and 1009B, respectively. One example of this conventional communication device is disclosed in International Publication No. WO01/93442.
FIG. 12 is a block diagram showing a structure of another conventional communication device, and more specifically, a block structure of a UWB communication device. The block diagram of FIG. 12 shows transmitter power control, which equalizes the electric power levels of signals that a communication device receives from a plurality of partner communication devices in the following manner. The communication device receives a reception signal from a partner communication device and returns the reception power level information obtained from the reception signal, thereby changing the transmission power depending on the partner communication device.
The transmitter power control is a technique not unique to UWB but used widely for wireless communication, and FIG. 12 shows one example of the application of transmitter power control to UWB. In the communication device of this conventional example, receiver 2201 receives impulse trains transmitted from a plurality of other communication devices (unillustrated) via antenna 2205, and measurer 2202 measures the reception characteristics. Measurer 2202 includes signal-to-noise ratio measurer 2202A, reception signal intensity measurer 2202B, and error rate measurer 2202C.
These measurement results are used to detect the communication device that is required to control its transmission level. Information S2202, which indicates the detected communication device, is outputted to transmission-level-control-information generator 2203. Transmission-level-control-information generator 2203 generates transmission level control information S2203 to control the transmission level of the detected communication device, and transmitter 2204 transmits this information. This results in the control of the transmission level of the communication device that has received the transmission level control information. As a result, the reception characteristics of the impulse trains received from the plurality of other communication devices become equal to each other. This enables receiver 2201 to receive impulse trains transmitted concurrently from the plurality of other communication devices. An example of this conventional communication device is disclosed in Japanese Patent Unexamined Publication No. 2003-51761.
However, the conventional structure of International Publication No. WO01/93442 mentioned above includes a plurality of receiving systems and adjusts sync timing based on the correlation as described earlier. The structure requires that a plurality of receiving system signals be processed at high speed in a complicated decision flow. This might cause the receiver configuration to be complicated and large, thereby increasing the power consumption and price of the device. This is particularly difficult to achieve in a slave communication device such as a portable device. On the other hand, the conventional structure to control transmission power as described in Japanese Patent Unexamined Publication No. 2003-51761 mentioned above can reduce problems such as the inability to adjust sync timing due to signal interference (inability to pull into synchronism) and jitter increase during synchronization tracking. This structure, however, may still cause the receiver configuration to be complicated and large, thereby increasing the power consumption and price of the device. This is particularly difficult to achieve in a slave communication device such as a portable device.